1. Technical Field
The inventive arrangements relate generally to methods and apparatus for controlling composite structure deformation, and more particularly to the use of post cure techniques for controlling distortion caused by bulk temperature changes.
2. Description of the Related Art
Composite structures are widely utilized in a variety of devices and systems, including spaced based applications. However, variations in temperature can result in distortion of the structural components manufactured from such composite materials. For example, in the case of composite beams, torsional twisting about the longitudinal axis of the beam may occur due to variations in the coefficient of thermal expansion among the various plys. Such twisting can be intensified due to errors in the laminate ply angles which may occur due to imperfections in the manufacturing process.
Twisting distortions in composite beams can be a serious problem, particularly in high precision space based applications where bulk temperature variations are common. For example, when composite tube beams are used for antenna reflector applications, such twisting can cause reflector distortion, which in turn may cause mis-pointing and de-focusing of the reflector. According, distortion of composite beams can be a serious problem and may significantly reduce the overall performance of the corresponding system.
Several attempts have been made to develop composite beams suitable to withstand bulk temperature changes without twisting or distortion. For instance, efforts have been made to reduce the ply angle errors in the composite tubes by holding tighter tolerances during the manufacturing process. However, the manufacturing of composite beams inherently includes a certain minimal amount of ply angle errors. Additionally, higher manufacturing tolerances require great care be taken during the manufacturing process. Consequently, this method can be extremely expensive and time consuming while still resulting in beams which may distort.
Other efforts to produce satisfactory composite beams include building several component beams and subsequently measuring the twist or distortion of each one. Composite beams having minimal twist can then be selected for usage, while the remaining ones are discarded. In addition to being expensive, this process is wasteful and results in the manufacturing of several inadequate composite beams.
Occasionally, there may also be instances where it is desirable to intentionally cause a composite beam to twist to a predetermined extent in the event of a bulk temperature change. Such twisting may be used, for example, to counteract the effects of temperature distortion associated with other mechanical components in the system. In such instances, it is desirable to selectively cause the beam to twist in a controlled manner for a given temperature change. Accordingly, there exists a need for a method and apparatus of controlling composite beam that does not depend on ply angle and is simple to use on existing composite beams.
The invention concerns a method and system for controlling distortion in a beam caused by temperature changes. The method of the invention includes the steps of determining a desired amount of twist control needed for applying a twisting force to the beam in response to a temperature variation. A wrap is selected for providing the desired twist control of the beam. The wrap comprises a wrap material type, a wrap cross-sectional profile, and a selected wrap angle. The wrap is positioned on the beam in a helical pattern using the selected wrap angle and then attached to the beam. The twist control can be used to reduce beam twist increase beam twist.
The wrap can be bonded to the outer surface of the beam using a resin adhesive. For example, the resin adhesive can be an epoxy. According to a preferred embodiment, the resin adhesive is selected for curing without substantial heating.
The wrap material type can be isotropic provided that the wrap cross-sectional profile is selectively chosen to provide the desired characteristics. For example the wrap material type can be at least partially comprised of metal. For isotropic materials the wrap profile is particularly important. A wrap height, measured from the surface of the beam, which is approximately as large as a width of the wrap has been found to provide good results in this regard. For example, the wrap cross-sectional profile can be round.
The invention is particularly well suited for beams of a composite construction that are known to sometimes twist due to thermal distortions.
The selection of the wrap can be an iterative process whereby a twist control applied by a proposed wrap is calculated and compared to the desired amount of twist control. Further, this iterative process can include modifying at least one of a wrap material, wrap cross-sectional profile, and wrap angle and re-calculating the twist control applied by the wrap as modified to determine if it provides the desired amount of twist control obtained thereby until satisfactory results are achieved.
Notably, the selection of the wrap material can comprise selecting a wrap structural member and a wrap bonding agent. Further, two or more such wraps can be applied to the beam for obtaining the desired amount of twist control.
According to an alternative embodiment, the invention also concerns a twist control system for controlling distortion in a beam caused by temperature changes. The invention is particularly useful in the case of a beam having an inherent amount of temperature induced twisting associated therewith. A wrap, comprising a wrap material type, a wrap cross-sectional profile, and a wrap angle are helically bonded to the beam. The wrap material, wrap cross-sectional profile and wrap angle are selectively chosen for providing a desired twist control of the beam. The twist control applies a predetermined twisting force to the beam in response to a temperature change. The wrap can be used to eliminate an inherent amount of temperature induced twisting of the beam is eliminated by the wrap. As noted above, the wrap can be comprised of a structural member and a bonding agent. For example, the structural member can be a metal wire and the bonding agent can be an epoxy resin. Multiple wraps can likewise be used wherein each of the wraps are selectively chosen for the beam to provide the desired twist control.